1. Field of the Invention
This invention relates to early-rain-resistant joint-sealing compounds containing
(a) aqueous polymer dispersions (I), PA1 (b) nonionic cellulose ethers (II) selected from the group consisting of hydroxyethyl, hydroxyethyl-methyl, hydroxypropyl-methyl and hydroxypropyl cellulose, and PA1 (c) optionally typical additives, such as fillers, pigments, plasticizers, extenders, thickeners, foam inhibitors, dispersion aids, pH regulators, preservatives and anti-aging agents, which can be produced by thorough mixing of (I) with the other constituents; to a process for the production of these joint-sealing compounds and to their use. PA1 (a) aqueous polymer dispersions (I), PA1 (b) nonionic cellulose ethers (II) selected from the group consisting of hydroxyethyl, hydroxyethyl-methyl, hydroxypropyl-methyl and hydroxypropyl cellulose, and PA1 (c) optionally typical additives, such as fillers, pigments, plasticizers, extenders, thickeners, foam inhibitors, dispersion aids, pH regulators, preservatives and anti-aging agents, PA1 (a) 25 to 90% by weight polymer dispersion, in the case of highly filled joint-sealing compounds, more particularly, 25 to 40% by weight polymer dispersion, PA1 (b) 0 to 60% by weight, and more particularly, 2 to 60% by weight fillers, PA1 (c) 0 to 1% by weight and more particularly, 0.3 to 0.5% by weight, wetting agents, PA1 (d) 0 20% by weight, and more particularly, 5 to 15% by weight, plasticizers, PA1 (e) 0 to 10% by weight, and more particularly, 4 to 6% by weight other typical additives, such as thickeners, foam inhibitors and pigments, and PA1 (f) up to 1.5% by weight cellulose ethers, all percentages by weight based in each case on the total quantity.
2. Discussion of Related Art
Joint-sealing compounds are known to the expert and have been successfully used in practice. Problems are involved in the use of joint-sealing compounds in applications where there is a possibility or danger of the joint-sealing compound coming into contact with water, for example spray water or rain, before curing. Thus, many of the joint-sealing compounds hitherto used, including those designed for outdoor application, are completely or partly washed out by heavy rainfall beginning shortly after their application. The use of nonionic cellulose ethers in joint-sealing or coating compounds based on acrylate dispersions is known from German Patent 38 14 078-A-1. The use of certain cellulose ethers in these compounds is said to improve wash-out behavior under the effect of water, such as rain water, and also smoothing behavior. The quantities in which the cellulose ethers are used in German Patent 38 14 078-A-1 are based on the solids content of the acrylate dispersion. There is no explicit reference to the ratio of "free" water to the cellulose ethers. Although it is clear from the Examples that the constituents mentioned were mixed in a planetary mixer for the production of a joint-sealing compound, there is no indication of the form or the order in which the individual constituents are mixed with one another.
However, it has been found in practice that, with early-rain-resistant joint-sealing compounds of the type in question, the individual constituents cannot be added in just any order or in just any form in the production of the joint-sealing compounds. For example, although the cellulose ethers mentioned can be scattered in small quantities into certain polymer dispersions and dissolved therein on a laboratory scale, the same does not apply on a production scale and certainly not in quantities which, based on the "free" water, are too large to obtain complete dissolution. If such an attempt is made, clumping or breaking of the dispersion consistently occurs. Although it is sometimes possible to rehomogenize the cellulose ether clumps, it is not possible to redisperse dispersion particles once they have coagulated. It is also not apparent to the expert from German Patent 38 14 078-A-1 that early-rain-resistant joint-sealing compounds of the type in question can be produced with other aqueous polymer dispersions than the acrylate dispersions mentioned therein. Nonionic cellulose ethers are also known as constituents of coating compounds and paints, for example of the type based on aqueous dispersions of organopolysiloxanes, as described in German Patent 12 84 007, or of the type based on vinyl acetate-maleic acid dibutyl ester dispersions, as described in German Patent 21 08 365. However, there is nothing in either of said publications to indicate to the expert that cellulose ethers of the type in question would also be suitable for joint-sealing compounds based on the same polymer dispersions as to lead to the desired effects.
A roof coating compound containing a polyacrylate dispersion as binder and hydroxyethyl cellulose as thickener in addition to fillers and other auxiliaries is described in the journal Resin Review 35, 2. This coating compound is claimed to be particularly resistant to washout. However, this property is attributed to the special setting behavior of the polyacrylate emulsion specially developed and used for coating compounds of the type in question. Thus, it was not logical to the expert to use hydroxyethyl cellulose for improving early rain resistance in joint-sealing compounds.
In addition, coating compounds do not satisfy the demands made of joint-sealing compounds, more particularly as laid down in DIN 52 456 "Bestimmung der Verarbeitbarkeit von Dichtstoffen (Determination of the Processability of Sealants)" and in DIN 52 454 "Standvermogen (Stability)".
In regard to stability in particular, joint-sealing compounds, unlike sealing compounds, are required to have the property of running only slightly, if at all, from a U-profile filled with the compound which, after filling, is placed in an upright position. Coating compounds are generally of lower viscosity because, on the one hand, they are designed for application by spray-coating or roll-coating and, on the other hand, are intended to show a certain flow for levelling of the compound. Although, in principle, joint-sealing compounds and coating compounds may be produced from the same constituents and although it should also be possible to produce a tolerably, useful coating compound by dilution of a joint-sealing compound, the converse does not necessarily apply.
It is known from Ullmann, Enzyklopadie der technischen Chemie, 4th Edition, Vol. 9, Verlag Chemie, Weinheim/BergstraBe 1974, pages 208-209, that nonionic cellulose ether derivatives, such as hydroxyethyl cellulose (HEC), hydroxyethyl methyl cellulose (HEMC) and hydroxypropyl methyl cellulose (HPMC), are used in polymeric plasters and emulsion paints inter alia for improving water retention power, open time, wet adhesion and thickening and setting behavior. However, there is nothing to indicate to the expert that cellulose ethers such as these in joint-sealing compounds lead to an improvement in spreadability, smoothing behavior and resistance to spray water of uncured surfaces of these compounds. In addition, paints, such as emulsion paints, and polymeric mortars are different materials from, and cannot be compared with, joint-sealing compounds. Thus, although polymeric plasters may possibly be used for filling joints, they generally do not have pronounced sealing properties and, in contrast to joint-sealing compounds, can be divided into portions and applied by trowel.
The problem addressed by the present invention was to provide joint-sealing compounds based on polymer dispersions which, in addition to good smoothing behavior, would show early rain resistance before curing without any adverse effect on other desirable properties, such as modulus of elasticity, elongation at break and resilience, or on resistance to migration and freedom from coagulates and specks. Another problem addressed by the invention was to provide a process which would enable compounds such as these to be produced.